The present invention relates to a sheet receiving and stacking apparatus for receiving and stacking plastic sheets and other kinds of paper which are rectangular sheets and, more particularly, to a delivery apparatus in an image forming apparatus such as a printing apparatus.
Generally, as a sheet receiving and stacking apparatus for receiving and stacking rectangular sheets, a delivery apparatus provided at the discharge section of a printing apparatus has been known. This type of delivery apparatus 1, as shown in FIG. 1, commonly has a base table 6 for receiving printed paper 3, a pair of parallel side boards 4, 4 provided nearly vertically on both sides of the base table 6 in a direction of receiving of the paper 3, and an end plate 5 provided at the forward end of the base table 6 in the direction of reception of the paper 3. Both side edges of the printed paper 3 discharged out of the printing section of the printing apparatus 2 are received between the two side boards 4, 4 which are disposed parallel, generally equal to the width of the printed paper 3. The leading edge of the ejected paper 3 strikes the end plate 5 located at front and floats down to be stacked on the base table 6.
In such a delivery apparatus 1, when printing is performed at a low image-printing rate on the paper 3, that is, in the case of a small amount of printing ink to be transferred to the paper 3, the paper 3 is discharged out of the printing apparatus 2 without changing its flat form therefore there will occur no problem about the stacking of the paper 3 in the delivery apparatus 1. However, in the case of a high image-printing rate, for example when much of ink has been transferred to the paper 3 as in solid printing, the upper surface of the paper 3 to which the ink has been transferred extends largely, curling largely downwardly into an upwardly swollen form. The paper 3 discharged out of the printing apparatus 2, therefore, will be stacked in a disorderly fashion on the base table 6.
To solve this problem, there has been a printing apparatus 7 of known art which, as shown in FIG. 2, is provided with an auxiliary paper discharge member 8 at the entrance of the delivery apparatus 10 mounted in the paper delivery section. This auxiliary member 8 holds upwardly both side edges of the paper 9 in a direction of travel of the paper 9 that has been discharged out of the printing apparatus 7, bending the paper 9 into a form of a U letter in the delivery state to thereby provide the paper 9 with stiffness and to thereby prevent the paper 9 from being largely curled with the effect of ink and stacked on the delivery apparatus 10 in a disorderly fashion.
Another apparatus which curves paper into a U-letter form has been disclosed in Japanese Utility Model Laid-Open No. Hei 5-10367. This apparatus has a pair of side plates disposed to face each other at a spacing on the delivery table, a pair of guide members provided on the pair of side plates so disposed as to face each other and protrusible on the delivery table, and guide members driving means for driving the guide members by turning the guide members simultaneously with the delivery operation of the image forming apparatus.
The prior art delivery apparatus described above, however, has such a problem that both side edges of the paper 9 are partly held upwardly when the aforesaid auxiliary paper discharge member 8 is employed, but other portion of the paper 9 apart from the auxiliary paper discharge member 8 becomes free; the paper 9, therefore, is still affected by the ink to curl largely with the ink, resulting in unevenly stacked paper.
In the delivery apparatus in which the guide members provided on the side plates are forced to move in and out by the guide member driving member in synchronization with the delivery of paper from the image forming apparatus, it is difficult to control the guide member driving means in accordance with the hardness of the paper, or a difference in the stiffness of the paper, which is determined by a difference in thickness and weight which depend upon the kind of the paper. Besides, the construction of the delivery apparatus required for mounting the guide member driving means will become complicated, which will cause a trouble to occur and raise a manufacturing cost.